A large literature suggests that the majority of "uncontrolled" hypertensives are under medical care, and that lack of control is largely explained by physicians not intensifying treatment to achieve the blood pressure targets recommended in the national guidelines. Traditional physician education, feedback, and reminders have a limited effect in promoting a rapid rate of guideline implementation. The theoretical framework of diffusion of innovations suggests that providing physicians with tools to reduce uncertainty about the attributes of a guideline may accelerate the adoption process. The presumed barriers to treatment intensification for uncontrolled hypertension are: 1) uncertainty over the patient's "true" blood pressure; 2) uncertainty over whether the patient is adherent to medications already prescribed; and 3) uncertainty over the benefits of adding medications when patients express preference for lifestyle modification. We will conduct a cluster randomized trial in 10 primary care clinics (5 intervention and 5 control) to test the hypothesis that an intervention based on diffusion of innovations theory, and targeting provider treatment actions, will increase the prevalence of blood pressure control to JNC 7- recommended levels in African- American patients (< 140/90 mm Hg or < 130/80 mmHg if the patient has diabetes). The uncertainty reduction tools in the proposed "Uncertainty Reduction to Accelerate Diffusion (URAD)" practices will include: 24-hour ambulatory blood pressure monitoring, electronic bottle-cap monitoring of medication adherence, and medication and lifestyle counseling. The "Usual Practice (UP)" physicians will receive education about the guidelines and a "placebo" chart form indicating the patient is being followed in a blood 3ressure control study. The 10 participating clinics represent a large, multi-site private group practice and a 3ublic health care system. Sixty-seven patients per clinic (670 total) will be enrolled when the intervention is initiated, and their blood pressure and self-reported medication and lifestyle adherence will be monitored for two years. Sixty percent of the sample will be African-American, and the study will have 90% power to detect a difference of 20% in the prevalence of hypertension control in the African-Americans as a result of the intervention (50% control in URAD clinics vs. 30% control UP clinics). Secondary endpoints will include blood pressure measurements by study staff under standardized conditions, physician treatment intensification actions, patient adherence, characteristics of doctor-patient communication associated with treatment action, use of the URAD components, and physician knowledge and beliefs about the JNC 7 guidelines and their relationship to blood pressure control. Analysis of secondary endpoints will include race. The research team has collaborated with both health systems in previous studies, and is experienced in conducting hypertension control and behavioral intervention studies in the target population.